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  1. #61
    holmburgers's Avatar
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    Hi Kirk,

    Well I'm a graduate of KU, but I honestly have been toying with the idea of auditing some chemistry courses next semester.

    I understand acoustic resonance of course, but in this context it's unclear how to conceptualize it. It sounds like the key to a good sensitizing dye is that it "becomes one" with the silver-halide crystal? What's the other option, that they're just sitting next to each other? Simplified, I know...
    If you are the big tree, we are the small axe

  2. #62
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    The dye "becomes one" with the crystal is a good way to put it!

    The resonance of the electrons and the plus charge on the Nitrogens help in this. In the eye, similar dyes cause color vision, but they have fat tails to anchor them to the retina although they still have the charged Nitrogen IIRC.

    PE

  3. #63
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    Is this the kind of resonance we're talking about? -> http://en.wikipedia.org/wiki/Electron_Spin_Resonance
    If you are the big tree, we are the small axe

  4. #64
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  5. #65
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    ahh.. thanks!
    If you are the big tree, we are the small axe

  6. #66

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    In addition to PE's link to resonance, follow up with this on on conjugation - the resonance is needed to get an photon absorbed into the molecule, which then needs this property:
    http://en.wikipedia.org/wiki/Conjugated_system

    Resonance is needed to help absorb a photon and allow an electron to move about the molecule. The conjugation helps distribute the charge of the electron about the area of conjugation. The longer the area of conjugation, the more the charge is distributed. Also, the length of the conjugated chain the longer the wavelength of light that can be absorbed. That is, a blue dye will be shorter in length than a red dye. And IR dye will be longer yet.

    Then check this:
    http://en.wikipedia.org/wiki/Cyanine

    And look at the molecules PE showed in Post #33. You can see how the longer the chain of conjugated carbons in those molecules affect the wavelength of absorption.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  7. #67
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    Kirk;

    Thanks for the clarification and extension. It really will help everyone understand this stuff which otherwise is arcana to most.

    PE

  8. #68
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    Thanks to both you guys. I'm gonna catch up on this reading today.

    Kirk's description is just the kind of thing for someone such as myself. My understanding of chemistry is basically nil, but I do, like most, have an understanding of physics and can conceptualize systems like this. It takes someone who gets it to say it in such an illuminatory manner.

  9. #69
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    Quote Originally Posted by Athiril View Post
    A thought occurred to me.. can we just recycle the dyes that get washed out of a commercial film in a pre-wash?
    When I was looking at my discolored developer the other night this quote came back to my memory.

    The next post was PE saying, well how the heck are you gonna separate out the sensitizing dyes? A fair question, but what if it's not necessary to do that? Then there were a fair number of intelligent people saying, what seemed to me, to be intelligents things, but I'd rather fly in the face of all of that a re-assert this proposition!



    So lets say we do a really thorough pre-wash in distilled water and evaporate all the liquid. The remaining powder should contain sensitizing dyes, along with other dyes and _________. (what else?)

    You guys say that the dyes are ionic, so does that mean they're easily destroyed?

    I don't know, maybe I'm just spinning wheels, but it seems like such a good idea. And of course who can really say whether it works or not until somebody actually tries it... but "what ifs", "how comes" and "why nots" aside, what do you guys think?

    GO!

  10. #70
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    Chris;

    That mix will be about 90% absorber dyes and 10% sensitizing dyes, if that. The sensitizing dyes were designed to stick to the grains and that is why some films end up pink! The dyes (some of them) come out slowly or in the fix or final wash.

    Other things present in the pre-wet are tetra-aza-indede or similar compounds, metal complexes (very low concentration), antifoggants and surfactants.

    PE



 

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